H2(v=3)+H2(He)碰撞中的转动能量转移

激发态Na2与H2碰撞,使H2(v=3,J=3)得到布居,在H2和He总气压为800Pa及温度为700K的条件下,利用相干反斯托克斯拉曼散射（CARS）光谱技术研究了H2(3,3)与H2(He)间转动能量转移过程。改变CARS激光束与激发Na2的激光之间的延迟时间,测量He不同摩尔配比时H2(3,J)态CARS谱强度的时间演化,得到H2(3,3)的总弛豫速率系数分别为=(21±5)×10-13cm3s-1和=(5.6±1.6)×10-13cm3s-1。测量H2(3,J)各转动态的相对CARS谱强度,由速率方程分析,得到H2(3,3)+H2→H2(3,J)+H2中,对于J=2,4,转移速率系数分别为11±4和8.2±3.1cm3s-1。在H2(3,3)+He→H2(3,J)+He中,对于J=2,4,转移速率系数分别为3.1±1.2和2.1±0.7cm3s-1。对于H2(3,3),单量子弛豫׀∆J׀=1约占该态总弛豫率的90%。     

Cs(6P)+(Ne,N2)碰撞能量转移

在气体样品池条件下,研究了Cs(6P3/2) (Ne,N2)碰撞能量转移过程.用调频半导体激光器激发Cs原子至Cs(6P3/2)态,在不同的Ne或N2气压下,测量了直接6P3/2→6S1/2荧光和转移6P1/2→6S1/2荧光,对于6P3/2与Ne的碰撞,电子态能量仅能转移为Ne原子的平动能.在与N2的碰撞中,向分子振转态的转移是重要的.利用速率方程分析,可以得到碰撞转移速率系数,对于Ne,6PJ精细结构碰撞转移速率系数为1.45×10-12cm3·s-1.对于N2,测量6P Ne和6P N2二种情况下荧光的相对强度比,确定精细结构速率系数为1.64×10-12cm3·s-1,6P态猝灭速率系数为4.88×10-12cm3·s-1.     

Cs(8S)态的碰撞转移和高位原子态的激发

在Cs蒸气中,二步激发Cs原子至8S态,研究了其碰撞转移和高位原子态的产生过程.在1016～1017 cm-3密度范围内,测量了碰撞激发转移8S 6S→6D 6S的速率系数.由测得的荧光强度随密度的变化关系,得到k6D=(2.4±0.5)×10-10 cm3·s-1.同时研究了碰撞能量合并过程5D 5D→nL 6S(nL=9D,11S,7F),5D态是由8S→7P→5D的辐射跃迁产生的.由以前测量过的6P 5D 6S 7D的转移速率系数以及6P态的原子密度,结合荧光强度比得到碰撞能量合并过程的速率系数,对于9D,11S和7F各态,其平均值分别为(6.4±3.2)×10-10,(1.0±0.5)×10-10和(8.4±4.2)×10-10 cm3·s-1.     

K-Cs混合蒸气中K(4P)+Cs(5D)碰撞能量合并

测量了K- Cs混合蒸气中碰撞能量合并过程K(4P) +Cs(5D)→Cs(6S) +K(4D ,6S)速率系数,测量是相对于已知速率系数的过程[即Cs(6P) +Cs(5D)→Cs(6S) +Cs(7DJ) ]进行的。利用激光光解K2 和Cs2分子,得到Cs(6P ,5D)和K(4P)态原子,探测直接由光解离产生的原子发射的与由碰撞转移而布居的原子激发态发射的荧光的相对强度,结合Cs(6P)和K(4P)态的有效寿命,得到异核碰撞能量合并速率系数分别为2. 6×10 -9和3 .6×10 -9cm3 ·s-1。讨论了其他过程对速率系数的影响。     

激发态Cs(5D)原子间碰撞能量转移

用激光二步激发Cs原子至8S态,从谱线的波长及强度可以确定Cs原子的辐射及碰撞过程,5D态主要是由8S→7P→5D跃迁布居的.在1016-1017Cs密度范围内,测量了碰撞能量合并5D 5D→nL 6S(nL=9D,11S,7F)速率系数,因5D→6P(3.0-3.6μm)处于红外本实验不能探测,利用一个已经测量过的过程(即6P 5D→6S 7D)作相对测量,对于9D,11S和7F态,其平均速率系数分别为(8.4±4.2)×10-10,(7.3±3.6)×10-10和(9.7±4.8)×10-10cm3s-1.讨论了碰撞转移过程11S 6S 7F 6S对速率系数的影响.     

激光激发Cs+H_2系统形成CsH分子机理的实验研究

在Cs-H2混合系统中用激光将Cs原子激发到6P3/2能级,研究了CsH分子的形成机制.利用光学吸收法得到6P3/2态的密度及其空间分布,能量合并过程6P3/2+6P3/2→6D+6S1/2产生6D态原子;猝灭过程Cs(6P3/2)+H2(v=0)→Cs(6S1/2)+H2(v=2)产生H2(v=2)态.由6P3/2态原子密度及6D→6P3/2与6P3/2→6S1/2的荧光比得到碰撞能量合并速率系数,在不同的H2密度下,测量了转移荧光强度I895,得到了H2(2,J)态的产生速率系数kH2(2,J)=1.     

Cs(6D_J)+(H_2,H_e)的反应与非反应碰撞能量转移

在样品池条件下,利用原子荧光光谱方法,测量了Cs(6DJ)与H2,He碰撞中的反应与非反应能量转移截面.利用脉冲激光886nm线双光子激发Cs(6S)到Cs(6D3/2)态,原子荧光中除含有6D3/2→6P的直接荧光外,还含有6D5/2→6P的转移荧光.利用三能级模型的速率方程分析,在不同的He和H2密度下,分别测垦直接荧光与转移荧光的时间积分荧光强度比,得到了6D3/2与H2和He碰撞的精细结构转移截面分别为σ=(55±13)×10-16和(16±4)×10-16 cm2,同时确定了6D5/2与H2和He的碰撞猝灭速率系数.6D5/2态与H2的碰撞猝灭速率系数比6D5/2与He的大,它是反应与非反应速率系数之和,利用实验数据确定非反应速率系数为6.3×10-10 cm3·s-1,得到6D5/2与H2的反应截面为(2.0±0.8)×10-16 cm2.利用不同H2(或He)密度下6D5/2→6P3/2时间积分荧光强度,得到6D3/2与H2反应截面为(4.0±1.6)×10-16 cm2,6D3/2与H2反应的活性大于6D5/2.     

碰撞能量转移Cs(6P)+Cs(5D)→Cs(6S)+Cs(nL=9S,5F)的截面测量

二步激发Cs原子至8S态,测量了碰撞转移过程Cs(6P)+Cs(5D)→Cs(6S)+Cs(nL=9S,5F)的截面,测量由7D,9S和5F态发射的荧光强度,从荧光强度比和σ(7D)值得到了σ(9S)和σ(5F),而σ(7D)已经进行过绝对测量,截面值σ(9S)和σ(5F)分别为8.7×10-15和1.3×10-14?cm2.讨论了能量转移过程9S+6S5F+6S对σ(9S)和σ(5F)的影响.     

Cs2分子的光解光谱

利用He-Cd激光器的441.6 nm线光解Cs2分子, 使Cs(n2L)(nL=7P, 6D)态得到布居, 在Cs密度1到9×1015 cm-3范围内测量原子荧光对分子荧光强度比, 得到碰撞转移率系数对解离率之比分别为2.9×10-17和7.4×10-18 cm3. 测定Cs nLJ对nLJ'荧光分支比, 得到72P, 62D态精细结构解离率之比分别为0.53和0.43. 从远翼激发得到的精细结构转移截面与从其他激发过程得到的截面结果相符, 给出了碰撞转移到6D态外(即Cs(6D)+Cs(6S)→Cs(6D)以外的态)的截面为1.9×10-14 cm2.     

Rb(5 P_J)+(He、N_2)碰撞能量转移

在气体样品池条件下,研究了Rb(5PJ) (He、N2)碰撞能量转移过程.调频半导体激光器稍微调离共振线,激发Rb原子至Rb(5P3/2)态,在不同的He或N2气压下,测量了直接5P3/2→5S1/2荧光和转移5P1/2→5S1/2荧光.对于5PJ与He的碰撞.电子态能量仅能转移为He原子的平动能.在与N2的碰撞中,向分子振转态的转移是重要的.利用速率方程分析,可以得到碰撞转移速率系数,对于He,5P3/2→5S1/2转移速率系数为2.23×10-12cm3s-1.对于N2,测量5PJ He和5PJ N2二种情况下荧光的相对强度比,利用最小二乘法确定5P3/2→5S1/2转移速率系数为4.38×10-11cm3s-1,5PJ态猝灭速率系数为5.45×10-11cm3s-1.与其他实验结果进行了比较.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.